Abstract: A failure diagnosis method for an inverter circuit, which easily performs failure diagnosis of a FET of the inverter circuit without delay includes comparing a motor terminal voltage corresponding to each phase of the inverter circuit including semiconductor switching devices (FETs) to drive a motor, with a threshold voltage by comparators as voltage comparison circuitry. At this time, the threshold voltage is changed according to a high-side FET and a low-side FET on which failure diagnosis is to be performed. Subsequently, by a digital output from the comparator, whether there is a short circuit of each FET of the motor terminal voltage is determined.